This invention relates to flat cable and in particular flat cable comprising a plurality of insulated conductors bonded to a metallic substrate.
Flat cables are well known and take several forms. In one form of flat cable a plurality of conductors are placed parallel to one another and are laminated between a pair of films which surrounds each conductor thereby insulating each conductor from its neighbors as well as forming the flat cable construction. The insulation of each individual conductor cannot always be controlled as precisely and reproducibly as desired.
Another form of flat cable addresses this issue and preinsulated conductors are bonded to a carrier film. The film is generally of a polymeric material similar to that of the insulation and in order to achieve a bond between the insulated conductors and the film, the film must be heated to about its melting point. At this temperature it is difficult to maintain the dimensions of the film and this can lead to improper alignment of the wires. Further, it has been found that with certain polymeric materials, for example polyvinylidene fluoride, the film becomes brittle when cooled following the bonding process. It is then difficult to separate an individual insulated conductor from the cable since the brittle film tends to break thereby destroying the cable. Also, the conductor generally then retains a strongly adherent residue of the brittle film. This tends to make it difficult to terminate the wire in a conventional connector. It is desirable to be able to peel the individual conductors from the film as cleanly as possible.
U.S. Pat. Nos. 4,625,074 to Cox, 4,767,891 to Biegon et al. and 4,678,864 to Cox describe attempts to obtain a flat cable having dimensional stability at elevated temperatures during the manufacture of the cable. These patents disclose the use of a carrier film comprising a laminate of an attachment layer of a first polymeric material and a dimensional stabilization layer of a material having a higher melting point than the first polymeric material. The attachment layer and the dimensional stabilization layer are joined together with an adhesive layer. In use, the flat cable can delaminate if the cable is subject to temperatures above the melting point of the adhesive layer.
U.S. Pat. No. 4,678,864 to Cox also discloses the use of a ground plane in the construction of a flat cable assembly. The ground plane is positioned between the flat cable and a plastic covering. The plastic covering is coated over a major portion of its surface with a release agent so that it can be readily separated from the cable. The ground plane itself is not bonded to the flat cable. The flat cable itself is of conventional structure comprising a supporting film and insulated wires and thus it would be difficult to peel individual insulated wires cleanly from the cable.